地堑地形对长偏移距瞬变电磁测深的影响研究

以地堑地形为代表讨论了地堑地形对长偏移距瞬变电磁测深法（LOTEM）的影响，考察了把电偶极子源放在其中不同位置时引起的瞬变电磁响应，数值模拟结果表明，当把源放在地堑中不同位置时，对LOTEM产生的影响程度也不同，其中以源放在地堑下坡处影响最大，放在上坡处影响最小，放在中间（台地）的影响介于其间。所有的情况都表明，无论把源放在地堑的什么位置，地形对LOTEM的影响都非常大，由于异常场随着偏移距增加衰减很缓慢，仅仅靠增加偏移距是不能消除地形的影响的。最后指出在进行LOTEM勘探部署时，尽量把激发源铺设在平坦之处将可以最大限度的减少地形的影响。

GRABEN TOPOGRAPHYIC EFFECTS TO THE LONG OFFSET TRANSIENT ELECTROMAGNETIC RESPONSES

The graben topography is designed to study the influence on the Long Offset Transient Electromagnetic (LOTEM). The effects of the graben topography to the LOTEM responses are detailedly discussed in this paper. It shows that the graben topography has significant influence for all the simulated models whatever the location of source in the graben topography. If the electric dipole source is located downslope the graben, the topographic effect is the largest. The influence of the topography is the smallest when the source locates in the upslope position and the influence is medium in the middle bottom of the graben. It is impossible to avoid the influence if only putting the receivers far away because of the large spatial effect of the topography. It concludes that the location of source is much more important and it should be put in an area as flat as possible.